Written by Amanda Coe, the miniseries will also feature Mark Bonnar, Adeel Akhtar, Lydia Leonard, Frances Tomelty and Rhashan Stone.
The British broadcaster touted the project as "a provocative, audacious thriller that puts women's lives at the heart of a gripping, insightful story about the values we live by and the choices we make."
"I am both relishing and daunted by the prospect of taking on this role; it's grown-up, steamy and of queasy moral complexity," Watson said in a statement Tuesday.
"Apple Tree Yard is that rare thing, a perfectly executed page-turner that's also a gripping exploration of the difficult moral choices we face in adult relationships," added Coe.
Watson's credits include The Book Thief and Gosford Park. Chaplin has appeared in Washington Square and Cinderella.